1. Field of the Invention
This invention relates to a method for removing phosphine from a gas stream. More particularly, small amounts of phosphine in a carbon monoxide gas stream are oxidized to phosphorus pentoxide, which may be recovered from the gas stream as phosphoric acid.
2. Description of the Prior Art
In the production of elemental phosphorus by the reduction of phosphate ore in an electric furnace, the phosphorus-containing gases removed from the furnace are first passed through an electrostatic precipitator to remove particulate impurities and then cooled to condense the phosphorus vapor. The phosphorus-free furnace gas remaining after such treatment typically contains 90-92% by volume carbon monoxide along with small amounts of nitrogen, hydrogen, oxygen, carbon dioxide, water and phosphine (PH.sub.3), the latter being present in a concentration of less than 1%.
Since this carbon monoxide furnace gas has value as a fuel, a simple, low-cost method for removing the small amounts of phosphine from the furnace gas is desirable. Such a method would eliminate the possible formation (and unwanted deposition), when the gas is burned, of reaction products like red phosphorus, metaphosphoric acid, or meta- and orthophosphates and would thus enhance the usefulness of the carbon monoxide furnace gas as a fuel source.
Phosphine is known to react chemically with oxygen to form a variety of reaction products; see Van Wazer, Phosphorus and Its Compounds, Interscience Publishers Inc., New York, 1958 at pp. 191-192. The oxidization of elemental phosphorus (P.sub.4) present in carbon monoxide gas is taught by Frear in U.S. Pat. No. 2,374,188. However, methods for selectively oxidizing phosphine in carbon monoxide gas have not previously been reported in the literature.